During the past year, the laboratory has succeeded in purifying to homogeneity small amounts (10 to 50 micrograms) of the plasminogen activator (PA) from Rous sarcoma virus-transformed chicken embryo fibroblasts (RSVCEF). A synergistic enhancement of PA production brought on by treatment of RSVCEF with the tumor promoter phorbol myristic acetate (PMA) has provided an enriched source of PA (serum-free culture fluid from the PMA-treated RSVCEF cultures). The purification steps include affinity chromatography, ion exchange and gel filtration chromatography and polyacrylamide gel electrophoresis. The biochemical characterization and the use of the enzyme in add-back experiments await the production of larger quantities of PA. In order to accomplish this, antibody against the enzyme is now being produced so that a monospecific antibody linked to Sepharose can be employed for large-scale purification. In addition, the antibody will serve as a probe to examine the role of PA in malignant transformation. The mechanism of how a tumor promoter (PMA) can synergistically elevate a transformation-specific enzyme is also under investigation. The RSVCEF system is ideal since: the production of PA is closely correlated with malignant transformation; the cells are extremely sensitive to PMA; and an antibody to the purified enzyme will soon be available.